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Dynamical fragment productionin non-central heavy-ion collisions
E*, J
PLF*
TLF*
Sylvie Hudan, Indiana University
Evaporation Binary breakup fragmentation
See R.T. de Souza on Friday
Binary breakup : dynamical effect
F. Bocage et al., NP A676, 391 (2000)J. Normand, PhD Thesis, université de Caen (2001) S. Piantelli et al., PRL 88, 052701 (2002)B. Davin et al., PRC 65, 064614 (2002)
• U+C at 24 MeV/n : aligned/binary 3%• U+U at 24 MeV/n : aligned/binary 20%• Xe+Sn at Ebeam > 40 MeV/n : aligned/binary 70%
Large cross-section
See J. Colin in this session
Large asymmetries
LH
LH
ZZ
ZZasymmetry
1
0.5
Nor
mal
ized
sca
le
Experimental setup
Ring Counter :Annular Si (300 m) – CsI(Tl) (2cm)2.1 lab 4.21 unit Z resolutionMass deduced†
LASSA : Mass resolution up to Z=97 lab 58
Detection of charged particles in 4† : Modified EPAX K. Sümmerer et al., PRC 42, 2546 (1990)
Beam
114Cd + 92Mo at 50 A.MeV
Selected events : 2 fragments (Z4) detected in the Ring Counter
Reconstruction of the PLF* : PLF* Heavy + Light ZPLF*, APLF*, vPLF*
Characteristics of the selected events
Correlation between ZPLF* and the total multiplicity
Selection of peripheral events
Asymmetry of the angular distributionsPLF* frameHeavy
Heavy more forward focused
Distinction of 2 cases : forward and backward
6 Nc 10
PLF*v
Heavy emitted backward to the PLF*
PLF*v
Heavy emitted forward to the PLF*
backward
forward
Deviation from standard statistical fissionB. Davin et al., PRC 65, 064614 (2002)
Different charge correlation
In both cases ZPLF* 41
Peak at Z=6 §§ : Consistent with Montoya et al., PRL73, 3070 (1994)
6 Nc 10
Different asymmetry
LH
LH
ZZ
ZZη
backward
forward
Deviation from standard statistical fission
Different relative velocities
Large effect ( 50%)
B. Davin et al., PRC 65, 064614 (2002)6 Nc 10
backward
forward
Viola systematics
Velocity dissipation
Similar vPLF* distribution
When selected on vPLF* :Different charge asymmetries
forward :
Strong asymmetry for all vPLF*
B. Davin et al., PRC 65, 064614 (2002)
6 Nc 10
backward : compatible with standard statistical fissionforward : dynamical features
backward
forwardvPLF*
E*, J
Z=6
backward forward
Velocity damping and excitation energy
Same trend for both cases
More dissipation and fluctuations as ZPLF* decreases
For a given size, less dissipation in the dynamical case
Anti-correlation
expected if vPLF* and (vPLF*) correlated to a common quantity
Same correlation
correlated to E*
Statistical
Dynamical
Dynamical
Statistical
Damping and excitation : fission case
Deviation from the Viola systematics (predominantly Coulomb) as damping increases
More fluctuations on the kinetic energy released in the fragments
As velocity damping increases, E* increasesvPLF* E*
39Z35 PLF*
Process probability : opening channel39Z35 PLF*
Dynamical process appear at lower velocity damping
Up to 10% of the cross-section in binary breakup
Dynamical
Statistical
1 fragment case (x 0.1)
Charge split and Coulomb cost39Z35 PLF*
LH
LH
ZZ
ZZη
Higher asymmetry for the dynamical case
Different Coulomb cost
Less damping required for the dynamical case
DynamicalStatistical
DynamicalStatistical
Kinetic energy transferred39Z35 PLF*
More kinetic energy in the fragments for the dynamical case
For a given velocity damping, difference of 20-30 MeV
Constant offset with velocity damping when Coulomb subtracted
Dynamical
Statistical
Observation of a dynamical component
Process with a large cross-section
As compared to standard fission, the dynamical process has: Lower E* threshold Large asymmetry (dependent on E*) Strong alignment Large kinetic energy in the 2 fragments, for all E* Constant (TKE-Coulomb) for all E*
AMD : descriptionAntisymmetrized Molecular Dynamics :
Microscopic approach to nuclear collision dynamics
• Slater determinant of Gaussian packets• TDVP Equation of Motion for centroids• Quantum branching processes
NN collisionsWave packet diffusion/shrinking
114Cd+92Mo @ 50 MeV/n : b = 0 - 9.2 fmDynamical calculation At t = 300 fm/c :
Clusterization (dR<5fm) Statistical decay
A. Ono et al., Prog. Theor. Phys. 87, 1185 (1992)A. Ono and H. Horiuchi, Phys. Rev. C59, 853 (1999)A. Ono, S. Hudan, A. Chbihi and J.D. Frankland, Phys. Rev. C66, 014603 (2002)
AMD : global features
For all impact parameters
PLF and TLF branches Fragment production at mid-rapidity
Large production of Z=5-6 at all v// (already before decay)
AMD : alignment
Heavy mostly forward peaked in the PLF* frame
High cross section :forward : /TOT
0.23backward : /TOT
0.10
We select events with 2 fragments (Z4) emitted forward to the CM
INDRA data, Gd+U @ 36 MeV/uF. Bocage et al., NP A676, 391 (2000)
Heavy
PLF* frame
backward
forward
AMD : charge asymmetry
forward: peaked at large asymmetry
backward: flat distribution
Cd+Mo @ 50 MeV/n B. Davin et al., PRC 65, 064614 (2002)
backwardforward
backward
forward
AMD : relative velocity
forward case is characterized by a higher relative velocity as compared to the backward case
10% effect (25% in the data)
Cd+Mo @ 50 MeV/nB. Davin et al., PRC 65, 064614 (2002)
backward
forward
AMD : Influence of the target
114Cd+12C @ 50 MeV/n
Few fragments produced at mid-rapidity
binary/tot < 2%
ConclusionsThe AMD calculations show the trends observed in the experimental data :
• alignment • asymmetry• relative velocity with a lower magnitude• influence of the target
A total of 8000 events have been calculated, representing 160000 cpuhours ( 18 years).Thanks to the UITS and RATS group at IU.
“This work was supported in part by Shared University Research grants from IBM, Inc. to Indiana University.”
Acknowledgments
S. Hudan , B. Davin, R. Alfaro, R. T. de Souza, H. Xu, L. Beaulieu, Y. Larochelle, T. Lefort, R. Yanez and V.
ViolaDepartment of Chemistry and Indiana University Cyclotron Facility,
Indiana University, Bloomington, Indiana 47405
R. J. Charity and L. G. Sobotka Department of Chemistry, Washington University, St. Louis, Missouri 63130
T.X. Liu, X.D. Liu, W.G. Lynch, R. Shomin, W.P. Tan,M.B. Tsang, A. Vander Molen, A. Wagner, H.F. Xi,
and C.K. Gelbke National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy,
Michigan State University, East Lansing, Michigan 48824
To the LASSA collaboration :
To A. Ono for the AMD calculations
To J. Colin for providing figures